Instant noodles are produced in such a manner that cut raw noodle strings are subjected to a predetermined treatment and then dried. The instant noodles are instant foods that can be reconstituted and eaten in such a manner that: boiling water is poured, and the noodles are left for several minutes; or the noodles are boiled in a pot or the like for several minutes. To improve this reconstitution property, the group of noodle strings is subjected to a steam-boiling step in a process of producing the instant noodles.
To execute the steam-boiling step, a steaming machine is installed in a noodle producing factory. At this time, to reduce an installation space, a plurality of stages may be formed in the steaming machine. To be specific, the group of noodle strings which is a target to be steam-boiled is conveyed on a conveyor so as to go and return plural times in the steaming machine in a longitudinal direction and is steam-boiled by steam introduced into the steaming machine while being conveyed. Various types of multistage steaming machines have been released.
Further, for the purpose of energy saving in recent years, a method of more efficiently utilizing the steam used in the steaming machine has been studied. For example, PTL 1 discloses a method in which: conveyors are provided at several stages in a steaming machine; superheated steam is used in the steaming machine; and leakage of the steam is prevented by making pressure in a steam chamber negative.